Weight loss help

Hi everyone. Recently I've noticed I've gained a lot of weight and over the course of one year I've gone from a size 6 to a size 12 and it's made me really self-conscious. I've tried eating healthy and exersising but the weight won't budge! I'm aiming to get a nice bikini body for summer for when I go on holiday. Has anyone got any tips on how I can loose this weight?